The invention described herein may be manufactured, licensed, and used by or for the U.S. Government.
1. Field of the Invention
The present invention relates to chemical vapor generators. More particularly, it relates to a continuous, low-concentration, low-volume chemical solid state vapor generator (SSVG) apparatus and a solvent-free method for continuous surface passivation and controlled release of adsorbed chemical vapors from a solid adsorbent article. The apparatus is designed to be used in conjunction with, and for the calibration of, chemical air monitors and detectors known in the art for the collection, measurement, and quantitative analysis of chemical vapors.
2. Description of the Related Art
Chemical agent detection devices and monitors have been developed for use in various industries. These devices are often used for military purposes, to detect and quantify chemical agents such as HD or mustard gas, nerve agents such as GB and VX, and other highly toxic chemical vapors and aerosols.
Chemical vapor generator systems have been used in the art for calibrating and testing the agent sensitivity of such chemical agent devices and monitors. Several methods have been developed for performing such tests and calibrations. These methods typically involve the generation of chemical vapors using liquid chemical agents. U.S. Pat. No. 4,069,701 teaches a self-contained system for generating a dilute agent vapor of a desired concentration for use in calibrating and testing the sensitivity of an agent point-source alarm. Air is flowed through a dilute liquid agent solution in a bubbler, thus creating the desired vapor, which is then used to calibrate the alarm. U.S. Pat. No. 5,728,927 teaches a system for generating a chemical agent air stream for testing chemical agent detection devices. Liquid chemical agent is contained in a delta tube, which is immersed in a temperature bath to generate a chemical vapor stream. However, such methods are undesirable in that they can suffer from an uncontrolled release of the chemical agent, and the potential of aerosol formation exists if proper procedures are not carefully observed. These processes are also inherently dangerous due to the potential of an environmental release of chemical agents from the breakage of their chemical containing glass containers.
It is known in the art to use chemical vapor generator systems together with ambient air concentration monitors that continuously draw metered air samples to be analyzed for chemical vapor analysis through sampling lines connected to a chemical detector. Although much effort has been devoted to reducing surface adsorption and chemical reactivity of chemical vapors in these sampling lines, all sampling lines suffer from some form of chemical retention of material due to surface interactions between the chemical vapor of interest and the surface through which it passes. During periods of little or no chemical concentration activity, ambient air drawn through the chemical-vapor monitor will continuously strip away surface adsorbed chemical materials. This creates active adsorption sites throughout the entire sampling system. If the sampling line is then exposed to a transient chemical vapor concentration containing the chemical vapor of interest, a portion of this chemical will be removed from the air to passivate those previously exposed adsorption sites. This will result in an underestimation of the true chemical concentration of the original transient chemical exposure.
It would therefore be desirable to devise a continuous surface passivation apparatus and method for generating chemical vapors, which provides a chemical concentration standard for detector calibration that does not require the transport of liquid chemicals in the field. It would also be desirable for such an apparatus and method to be safe and accurate, and generate no chemical waste, thus reducing costs.
The present invention provides a solution to these problems. The invention provides a chemical adsorption system including chemical adsorption apparatus comprising a temperature-controlled, non-permeable, non-reactive container having vapor inlet and outlet fittings. The container contains a solid adsorption article, which comprises a known amount of a chemical adsorbate material disposed on a solid micro-porous adsorbent material. A controllable source of inert gas is connected to an inlet line on one end of the container, and an outlet line is connected to the other end of the container. By controlling various parameters such as the temperature of the adsorption article, the amount of the adsorbate on the adsorbent, and the flow rate of inert gas through the container, the amount of chemical adsorbate material vapor that is released from the adsorbent can be precisely controlled and predicted. This invention contains no liquid chemical materials in its design.
The invention solves the problem of surface passivation by continuously releasing a trace amount of chemical vapor in a small volume of inert gas to the sampling inlet of a chemical vapor concentration monitor or detector. In this arrangement, the apparatus of the invention serves as both an internal chemical reference standard to the attached chemical vapor monitor and as a chemical surface passivator. The apparatus thus continuously passivates all of the contacted surfaces with the chemical of interest, including the sample transfer line leading up to the attached chemical vapor monitor as well as the entire chemically exposed sampling surfaces contained within the chemical monitoring system itself. This allows for improved mass transport of chemical vapors in sampling systems. As an added benefit, all of the material exiting the container can be consumed by the air sampling monitoring system, thus generating no chemical waste.
The invention is further advantageous in that it serves to deliver an internal calibration standard from the adsorbent article for the purpose of calibrating air concentration monitors and detectors. Furthermore, the invention is capable of spanning several orders of magnitude in chemical vapor concentration from the parts-per-million (ppm) to parts-per-trillion (ppt) range.
The invention provides a chemical adsorption system, or solid state chemical vapor generator system, which comprises:
a) a chemical vapor generating apparatus comprising a temperature controlled housing having an outer shell defining an interior chamber; a vapor inlet disposed through a first end of the housing; a vapor outlet disposed through a second end of the housing; and an adsorption article which comprises a chemical adsorbate material disposed on a solid adsorbent material, which adsorption article is contained within a gas impermeable container within the interior chamber of the housing which container is attached to the vapor inlet and vapor outlet, and which adsorption article is capable of releasing controlled amounts of chemical adsorbate material vapor into the gas impermeable container;
b) an inert gas source connected to the vapor inlet via a vapor inlet tube, which gas source is capable of supplying a predetermined amount of inert gas into the interior chamber of the housing and into the gas impermeable container, via the vapor inlet; and
c) a vapor outlet tube connected to the vapor outlet, through which vapor outlet tube the chemical adsorption apparatus is capable of releasing a predetermined amount of chemical vapor, together with a predetermined amount of inert gas, from the gas impermeable container and out of the housing.
The invention further provides a method for generating a chemical vapor gas stream, which comprises:
i) providing a chemical vapor generating system which comprises:
a) a chemical adsorption apparatus comprising a temperature controlled housing having an outer shell defining an interior chamber; a vapor inlet disposed through a first end of the housing; a vapor outlet disposed through a second end of the housing; and an adsorption article which comprises a chemical adsorbate material disposed on a solid adsorbent material, which adsorption article is contained within a gas impermeable container within the interior chamber of the housing which container is attached to the vapor inlet and vapor outlet, and which adsorption article is capable of releasing controlled amounts of chemical adsorbate material vapor into the gas impermeable container;
b) an inert gas source attached to the vapor inlet via a vapor inlet tube, which gas source is capable of supplying a predetermined amount of inert gas into the interior chamber of the housing via the vapor inlet; and
c) a vapor outlet tube attached to the vapor outlet, through which vapor outlet tube the chemical adsorption apparatus is capable of releasing a predetermined amount of chemical adsorbate material vapor, together with a predetermined amount of inert gas, from the gas impermeable container and out of the housing; and
ii) supplying a predetermined amount of inert gas from the inert gas source into the gas impermeable container; and wherein a predetermined amount of chemical adsorbate material vapor is released, together with a predetermined amount of inert gas, from the gas impermeable container and out of the housing, via the vapor outlet tube.
A solid-state chemical-vapor generating apparatus which comprises a temperature controlled housing having an outer shell defining an interior chamber; a vapor inlet disposed through a first end of the housing; a vapor outlet disposed through a second end of the housing; and an adsorption article which comprises a chemical adsorbate material disposed on a solid adsorbent material, which adsorption article is contained within a gas impermeable container within the interior chamber of the housing which container is attached to the vapor inlet and vapor outlet, and which adsorption article is capable of releasing controlled amounts of chemical adsorbate material vapor into the gas impermeable container.